UPWIND-DOWNWIND-CROSSWIND SEA-CLUTTER MEASUREMENTS.

Radar returns were collected nearly simultaneously on four frequencies-428 MHz, 1228 MHz, 4455 MHz, and 8910 MHz-for both linear and cross polarizations. In the course of these measurements, sea clutter was recorded in the upwind, downwind, and crosswind directions. The ratios of the upwind-to-downwind and upwind-to-crosswind returns were investigated as functions of the incident angle, the polarization, the radar wavelength, and the gross surface parameters of wind velocity and wave height. The upwinddownwind ratio is shown to decrease with increasing angle and surface roughness. Horizontal polarization is more sensitive to wind direction than vertical polarization. The short wavelengths are more sensitive to wind direction than the long wavelengths. The upwindcrosswind ratio remains significant as the short wavelengths for the roughest sea encountered at Puerto Rico. The results provide estimates of the upwind-downwind-crosswind relations as functions of the above parameters over an angular region of 4 to 90 degrees vertical incidence and from calm sea conditions to moderately rough conditions characterized by 5 - to 7-ft wave heights and 10 - to 20-knot winds. Author